package com.github.beihaifeiwu.myspring.template.velocity.view;

import com.github.beihaifeiwu.myspring.template.velocity.VelocityConfig;
import com.github.beihaifeiwu.myspring.template.velocity.VelocityConfigurer;
import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.VelocityEngine;
import org.apache.velocity.context.Context;
import org.apache.velocity.exception.MethodInvocationException;
import org.apache.velocity.exception.ResourceNotFoundException;
import org.apache.velocity.tools.generic.DateTool;
import org.apache.velocity.tools.generic.NumberTool;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.context.ApplicationContextException;
import org.springframework.core.NestedIOException;
import org.springframework.web.servlet.support.RequestContextUtils;
import org.springframework.web.servlet.view.AbstractTemplateView;
import org.springframework.web.util.NestedServletException;

import javax.annotation.Nonnull;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Locale;
import java.util.Map;
import java.util.TimeZone;

/**
 * View using the Velocity template engine.
 * <p>
 * <p>Exposes the following JavaBean properties:
 * <ul>
 * <li><b>url</b>: the location of the Velocity template to be wrapped,
 * relative to the Velocity resource loader path (see VelocityConfigurer).
 * <li><b>encoding</b> (optional, default is determined by Velocity configuration):
 * the encoding of the Velocity template file
 * <li><b>velocityFormatterAttribute</b> (optional, default=null): the name of
 * the VelocityFormatter helper object to expose in the Velocity context of this
 * view, or {@code null} if not needed. VelocityFormatter is part of standard Velocity.
 * <li><b>dateToolAttribute</b> (optional, default=null): the name of the
 * DateTool helper object to expose in the Velocity context of this view,
 * or {@code null} if not needed. DateTool is part of Velocity Tools.
 * <li><b>numberToolAttribute</b> (optional, default=null): the name of the
 * NumberTool helper object to expose in the Velocity context of this view,
 * or {@code null} if not needed. NumberTool is part of Velocity Tools.
 * <li><b>cacheTemplate</b> (optional, default=false): whether or not the Velocity
 * template should be cached. It should normally be true in production, but setting
 * this to false enables us to modify Velocity templates without restarting the
 * application (similar to JSPs). Note that this is a minor optimization only,
 * as Velocity itself caches templates in a modification-aware fashion.
 * </ul>
 * <p>
 * <p>Depends on a VelocityConfig object such as VelocityConfigurer being
 * accessible in the current web application context, with any bean name.
 * Alternatively, you can set the VelocityEngine object as bean property.
 * <p>
 * <p>Note: Spring 3.0's VelocityView requires Velocity 1.4 or higher, and optionally
 * Velocity Tools 1.1 or higher (depending on the use of DateTool and/or NumberTool).
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Dave Syer
 * @see VelocityConfig
 * @see VelocityConfigurer
 * @see #setUrl
 * @see #setExposeSpringMacroHelpers
 * @see #setEncoding
 * @see #setVelocityEngine
 * @see VelocityConfig
 * @see VelocityConfigurer
 */
public class VelocityView extends AbstractTemplateView {

    private Map<String, Class<?>> toolAttributes;

    private String dateToolAttribute;

    private String numberToolAttribute;

    private String encoding;

    private boolean cacheTemplate = false;

    private VelocityEngine velocityEngine;

    private Template template;


    /**
     * Set tool attributes to expose to the view, as attribute name / class name pairs.
     * An instance of the given class will be added to the Velocity context for each
     * rendering operation, under the given attribute name.
     * <p>For example, an instance of MathTool, which is part of the generic package
     * of Velocity Tools, can be bound under the attribute name "math", specifying the
     * fully qualified class name "org.apache.velocity.tools.generic.MathTool" as value.
     * <p>Note that VelocityView can only create simple generic tools or values, that is,
     * classes with a public default constructor and no further initialization needs.
     * This class does not do any further checks, to not introduce a required dependency
     * on a specific tools package.
     * <p>For tools that are part of the view package of Velocity Tools, a special
     * Velocity context and a special init callback are needed. Use VelocityToolboxView
     * in such a case, or override {@code createVelocityContext} and
     * {@code initTool} accordingly.
     * <p>For a simple VelocityFormatter instance or special locale-aware instances
     * of DateTool/NumberTool, which are part of the generic package of Velocity Tools,
     * specify the "velocityFormatterAttribute", "dateToolAttribute" or
     * "numberToolAttribute" properties, respectively.
     *
     * @param toolAttributes attribute names as keys, and tool class names as values
     * @see org.apache.velocity.tools.generic.MathTool
     * @see VelocityToolboxView
     * @see #createVelocityContext
     * @see #initTool
     * @see #setDateToolAttribute
     * @see #setNumberToolAttribute
     */
    public void setToolAttributes(Map<String, Class<?>> toolAttributes) {
        this.toolAttributes = toolAttributes;
    }

    /**
     * Set the name of the DateTool helper object to expose in the Velocity context
     * of this view, or {@code null} if not needed. The exposed DateTool will be aware of
     * the current locale, as determined by Spring's LocaleResolver.
     * <p>DateTool is part of the generic package of Velocity Tools 1.0.
     * Spring uses a special locale-aware subclass of DateTool.
     *
     * @see org.apache.velocity.tools.generic.DateTool
     * @see org.springframework.web.servlet.support.RequestContextUtils#getLocale
     * @see org.springframework.web.servlet.LocaleResolver
     */
    public void setDateToolAttribute(String dateToolAttribute) {
        this.dateToolAttribute = dateToolAttribute;
    }

    /**
     * Set the name of the NumberTool helper object to expose in the Velocity context
     * of this view, or {@code null} if not needed. The exposed NumberTool will be aware of
     * the current locale, as determined by Spring's LocaleResolver.
     * <p>NumberTool is part of the generic package of Velocity Tools 1.1.
     * Spring uses a special locale-aware subclass of NumberTool.
     *
     * @see org.apache.velocity.tools.generic.NumberTool
     * @see org.springframework.web.servlet.support.RequestContextUtils#getLocale
     * @see org.springframework.web.servlet.LocaleResolver
     */
    public void setNumberToolAttribute(String numberToolAttribute) {
        this.numberToolAttribute = numberToolAttribute;
    }

    /**
     * Set the encoding of the Velocity template file. Default is determined
     * by the VelocityEngine: "ISO-8859-1" if not specified otherwise.
     * <p>Specify the encoding in the VelocityEngine rather than per template
     * if all your templates share a common encoding.
     */
    public void setEncoding(String encoding) {
        this.encoding = encoding;
    }

    /**
     * Return the encoding for the Velocity template.
     */
    protected String getEncoding() {
        return this.encoding;
    }

    /**
     * Set whether the Velocity template should be cached. Default is "false".
     * It should normally be true in production, but setting this to false enables us to
     * modify Velocity templates without restarting the application (similar to JSPs).
     * <p>Note that this is a minor optimization only, as Velocity itself caches
     * templates in a modification-aware fashion.
     */
    public void setCacheTemplate(boolean cacheTemplate) {
        this.cacheTemplate = cacheTemplate;
    }

    /**
     * Return whether the Velocity template should be cached.
     */
    protected boolean isCacheTemplate() {
        return this.cacheTemplate;
    }

    /**
     * Set the VelocityEngine to be used by this view.
     * <p>If this is not set, the default lookup will occur: A single VelocityConfig
     * is expected in the current web application context, with any bean name.
     *
     * @see VelocityConfig
     */
    public void setVelocityEngine(VelocityEngine velocityEngine) {
        this.velocityEngine = velocityEngine;
    }

    /**
     * Return the VelocityEngine used by this view.
     */
    protected VelocityEngine getVelocityEngine() {
        return this.velocityEngine;
    }


    /**
     * Invoked on startup. Looks for a single VelocityConfig bean to
     * find the relevant VelocityEngine for this factory.
     */
    @Override
    protected void initApplicationContext() throws BeansException {
        super.initApplicationContext();

        if (getVelocityEngine() == null) {
            // No explicit VelocityEngine: try to autodetect one.
            setVelocityEngine(autodetectVelocityEngine());
        }
    }

    /**
     * Autodetect a VelocityEngine via the ApplicationContext.
     * Called if no explicit VelocityEngine has been specified.
     *
     * @return the VelocityEngine to use for VelocityViews
     * @throws BeansException if no VelocityEngine could be found
     * @see #getApplicationContext
     * @see #setVelocityEngine
     */
    protected VelocityEngine autodetectVelocityEngine() throws BeansException {
        try {
            VelocityConfig velocityConfig = BeanFactoryUtils.beanOfTypeIncludingAncestors(
                    getApplicationContext(), VelocityConfig.class, true, false);
            return velocityConfig.getVelocityEngine();
        } catch (NoSuchBeanDefinitionException ex) {
            throw new ApplicationContextException(
                    "Must define a single VelocityConfig bean in this web application context " +
                            "(may be inherited): VelocityConfigurer is the usual implementation. " +
                            "This bean may be given any name.", ex);
        }
    }

    /**
     * Check that the Velocity template used for this view exists and is valid.
     * <p>Can be overridden to customize the behavior, for example in case of
     * multiple templates to be rendered into a single view.
     */
    @Override
    public boolean checkResource(Locale locale) throws Exception {
        try {
            // Check that we can get the template, even if we might subsequently get it again.
            this.template = getTemplate(getUrl());
            return true;
        } catch (ResourceNotFoundException ex) {
            if (logger.isDebugEnabled()) {
                logger.debug("No Velocity view found for URL: " + getUrl());
            }
            return false;
        } catch (Exception ex) {
            throw new NestedIOException(
                    "Could not load Velocity template for URL [" + getUrl() + "]", ex);
        }
    }


    /**
     * Process the model map by merging it with the Velocity template.
     * Output is directed to the servlet response.
     * <p>This method can be overridden if custom behavior is needed.
     */
    @Override
    protected void renderMergedTemplateModel(@Nonnull Map<String, Object> model,
                                             @Nonnull HttpServletRequest request,
                                             @Nonnull HttpServletResponse response) throws Exception {

        exposeHelpers(model, request);

        Context velocityContext = createVelocityContext(model, request, response);
        exposeHelpers(velocityContext, request, response);
        exposeToolAttributes(velocityContext, request);

        doRender(velocityContext, response);
    }

    /**
     * Expose helpers unique to each rendering operation. This is necessary so that
     * different rendering operations can't overwrite each other's formats etc.
     * <p>Called by {@code renderMergedTemplateModel}. The default implementation
     * is empty. This method can be overridden to add custom helpers to the model.
     *
     * @param model   the model that will be passed to the template for merging
     * @param request current HTTP request
     * @throws Exception if there's a fatal error while we're adding model attributes
     * @see #renderMergedTemplateModel
     */
    protected void exposeHelpers(Map<String, Object> model, HttpServletRequest request) throws Exception {
    }

    /**
     * Create a Velocity Context instance for the given model,
     * to be passed to the template for merging.
     * <p>The default implementation delegates to {@link #createVelocityContext(Map)}.
     * Can be overridden for a special context class, for example ChainedContext which
     * is part of the view package of Velocity Tools. ChainedContext is needed for
     * initialization of ViewTool instances.
     * <p>Have a look at {@link VelocityToolboxView}, which pre-implements
     * ChainedContext support. This is not part of the standard VelocityView class
     * in order to avoid a required dependency on the view package of Velocity Tools.
     *
     * @param model    the model Map, containing the model attributes to be exposed to the view
     * @param request  current HTTP request
     * @param response current HTTP response
     * @return the Velocity Context
     * @throws Exception if there's a fatal error while creating the context
     * @see #createVelocityContext(Map)
     * @see #initTool
     * @see org.apache.velocity.tools.view.context.ChainedContext
     * @see VelocityToolboxView
     */
    protected Context createVelocityContext(
            Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {

        return createVelocityContext(model);
    }

    /**
     * Create a Velocity Context instance for the given model,
     * to be passed to the template for merging.
     * <p>Default implementation creates an instance of Velocity's
     * VelocityContext implementation class.
     *
     * @param model the model Map, containing the model attributes
     *              to be exposed to the view
     * @return the Velocity Context
     * @throws Exception if there's a fatal error while creating the context
     * @see org.apache.velocity.VelocityContext
     */
    protected Context createVelocityContext(Map<String, Object> model) throws Exception {
        return new VelocityContext(model);
    }

    /**
     * Expose helpers unique to each rendering operation. This is necessary so that
     * different rendering operations can't overwrite each other's formats etc.
     * <p>Called by {@code renderMergedTemplateModel}. Default implementation
     * delegates to {@code exposeHelpers(velocityContext, request)}. This method
     * can be overridden to add special tools to the context, needing the servlet response
     * to initialize (see Velocity Tools, for example LinkTool and ViewTool/ChainedContext).
     *
     * @param velocityContext Velocity context that will be passed to the template
     * @param request         current HTTP request
     * @param response        current HTTP response
     * @throws Exception if there's a fatal error while we're adding model attributes
     * @see #exposeHelpers(org.apache.velocity.context.Context, HttpServletRequest)
     */
    protected void exposeHelpers(
            Context velocityContext, HttpServletRequest request, HttpServletResponse response) throws Exception {

        exposeHelpers(velocityContext, request);
    }

    /**
     * Expose helpers unique to each rendering operation. This is necessary so that
     * different rendering operations can't overwrite each other's formats etc.
     * <p>Default implementation is empty. This method can be overridden to add
     * custom helpers to the Velocity context.
     *
     * @param velocityContext Velocity context that will be passed to the template
     * @param request         current HTTP request
     * @throws Exception if there's a fatal error while we're adding model attributes
     * @see #exposeHelpers(Map, HttpServletRequest)
     */
    protected void exposeHelpers(Context velocityContext, HttpServletRequest request) throws Exception {
    }

    /**
     * Expose the tool attributes, according to corresponding bean property settings.
     * <p>Do not override this method unless for further tools driven by bean properties.
     * Override one of the {@code exposeHelpers} methods to add custom helpers.
     *
     * @param velocityContext Velocity context that will be passed to the template
     * @param request         current HTTP request
     * @throws Exception if there's a fatal error while we're adding model attributes
     * @see #setDateToolAttribute
     * @see #setNumberToolAttribute
     * @see #exposeHelpers(Map, HttpServletRequest)
     * @see #exposeHelpers(org.apache.velocity.context.Context, HttpServletRequest, HttpServletResponse)
     */
    protected void exposeToolAttributes(Context velocityContext, HttpServletRequest request) throws Exception {
        // Expose generic attributes.
        if (this.toolAttributes != null) {
            for (Map.Entry<String, Class<?>> entry : this.toolAttributes.entrySet()) {
                String attributeName = entry.getKey();
                Class<?> toolClass = entry.getValue();
                try {
                    Object tool = toolClass.newInstance();
                    initTool(tool, velocityContext);
                    velocityContext.put(attributeName, tool);
                } catch (Exception ex) {
                    throw new NestedServletException("Could not instantiate Velocity tool '" + attributeName + "'", ex);
                }
            }
        }

        // Expose locale-aware DateTool/NumberTool attributes.
        if (this.dateToolAttribute != null || this.numberToolAttribute != null) {
            if (this.dateToolAttribute != null) {
                velocityContext.put(this.dateToolAttribute, new LocaleAwareDateTool(request));
            }
            if (this.numberToolAttribute != null) {
                velocityContext.put(this.numberToolAttribute, new LocaleAwareNumberTool(request));
            }
        }
    }

    /**
     * Initialize the given tool instance. The default implementation is empty.
     * <p>Can be overridden to check for special callback interfaces, for example
     * the ViewContext interface which is part of the view package of Velocity Tools.
     * In the particular case of ViewContext, you'll usually also need a special
     * Velocity context, like ChainedContext which is part of Velocity Tools too.
     * <p>Have a look at {@link VelocityToolboxView}, which pre-implements such a
     * ViewTool check. This is not part of the standard VelocityView class in order
     * to avoid a required dependency on the view package of Velocity Tools.
     *
     * @param tool            the tool instance to initialize
     * @param velocityContext the Velocity context
     * @throws Exception if initializion of the tool failed
     * @see #createVelocityContext
     * @see org.apache.velocity.tools.view.context.ViewContext
     * @see org.apache.velocity.tools.view.context.ChainedContext
     * @see VelocityToolboxView
     */
    protected void initTool(Object tool, Context velocityContext) throws Exception {
    }


    /**
     * Render the Velocity view to the given response, using the given Velocity
     * context which contains the complete template model to use.
     * <p>The default implementation renders the template specified by the "url"
     * bean property, retrieved via {@code getTemplate}. It delegates to the
     * {@code mergeTemplate} method to merge the template instance with the
     * given Velocity context.
     * <p>Can be overridden to customize the behavior, for example to render
     * multiple templates into a single view.
     *
     * @param context  the Velocity context to use for rendering
     * @param response servlet response (use this to get the OutputStream or Writer)
     * @throws Exception if thrown by Velocity
     * @see #setUrl
     * @see #getTemplate()
     * @see #mergeTemplate
     */
    protected void doRender(Context context, HttpServletResponse response) throws Exception {
        if (logger.isDebugEnabled()) {
            logger.debug("Rendering Velocity template [" + getUrl() + "] in VelocityView '" + getBeanName() + "'");
        }
        mergeTemplate(getTemplate(), context, response);
    }

    /**
     * Retrieve the Velocity template to be rendered by this view.
     * <p>By default, the template specified by the "url" bean property will be
     * retrieved: either returning a cached template instance or loading a fresh
     * instance (according to the "cacheTemplate" bean property)
     *
     * @return the Velocity template to render
     * @throws Exception if thrown by Velocity
     * @see #setUrl
     * @see #setCacheTemplate
     * @see #getTemplate(String)
     */
    protected Template getTemplate() throws Exception {
        // We already hold a reference to the template, but we might want to load it
        // if not caching. Velocity itself caches templates, so our ability to
        // cache templates in this class is a minor optimization only.
        if (isCacheTemplate() && this.template != null) {
            return this.template;
        } else {
            return getTemplate(getUrl());
        }
    }

    /**
     * Retrieve the Velocity template specified by the given name,
     * using the encoding specified by the "encoding" bean property.
     * <p>Can be called by subclasses to retrieve a specific template,
     * for example to render multiple templates into a single view.
     *
     * @param name the file name of the desired template
     * @return the Velocity template
     * @throws Exception if thrown by Velocity
     * @see org.apache.velocity.app.VelocityEngine#getTemplate
     */
    protected Template getTemplate(String name) throws Exception {
        return (getEncoding() != null ?
                getVelocityEngine().getTemplate(name, getEncoding()) :
                getVelocityEngine().getTemplate(name));
    }

    /**
     * Merge the template with the context.
     * Can be overridden to customize the behavior.
     *
     * @param template the template to merge
     * @param context  the Velocity context to use for rendering
     * @param response servlet response (use this to get the OutputStream or Writer)
     * @throws Exception if thrown by Velocity
     * @see org.apache.velocity.Template#merge
     */
    protected void mergeTemplate(
            Template template, Context context, HttpServletResponse response) throws Exception {

        try {
            template.merge(context, response.getWriter());
        } catch (MethodInvocationException ex) {
            Throwable cause = ex.getWrappedThrowable();
            throw new NestedServletException(
                    "Method invocation failed during rendering of Velocity view with name '" +
                            getBeanName() + "': " + ex.getMessage() + "; reference [" + ex.getReferenceName() +
                            "], method '" + ex.getMethodName() + "'",
                    cause == null ? ex : cause);
        }
    }


    /**
     * Subclass of DateTool from Velocity Tools, using a Spring-resolved
     * Locale and TimeZone instead of the default Locale.
     *
     * @see org.springframework.web.servlet.support.RequestContextUtils#getLocale
     * @see org.springframework.web.servlet.support.RequestContextUtils#getTimeZone
     */
    private static class LocaleAwareDateTool extends DateTool {

        private final HttpServletRequest request;

        LocaleAwareDateTool(HttpServletRequest request) {
            this.request = request;
        }

        @Override
        public Locale getLocale() {
            return RequestContextUtils.getLocale(this.request);
        }

        @Override
        public TimeZone getTimeZone() {
            TimeZone timeZone = RequestContextUtils.getTimeZone(this.request);
            return (timeZone != null ? timeZone : super.getTimeZone());
        }
    }


    /**
     * Subclass of NumberTool from Velocity Tools, using a Spring-resolved
     * Locale instead of the default Locale.
     *
     * @see org.springframework.web.servlet.support.RequestContextUtils#getLocale
     */
    private static class LocaleAwareNumberTool extends NumberTool {

        private final HttpServletRequest request;

        LocaleAwareNumberTool(HttpServletRequest request) {
            this.request = request;
        }

        @Override
        public Locale getLocale() {
            return RequestContextUtils.getLocale(this.request);
        }
    }

}